[requires php ^5.5 || ^7.0 -> your php version]でバージョンを変更しても別のエラーが出る場合の対処方法が知りたい。

提示コードですがエラーコードの通り7.0が必要ですと言われているのでそれに合わせて7.0を選ぶと今度は8.0が欲しいと言われてその繰り返しでエラーを対処できません。これはどうやって対処するのでしょうか？

composer

json
1{
2    "config": 
3    {
4        "platform-check": false,
5        "platform": {
6            "php": "7.0"
7        }
8    },
9
10    "require": 
11    {
12        "michelf/php-markdown": "1.9.1",
13        "ramsey/uuid": "4.2.2",
14        "laravel/laravel": "9.1.1"
15    }
16}

コマンド　composer config platform.php 8.0.2

shigurechan@shigurechan-System-Product-Name:~/prg/html$ composer update
Composer is operating significantly slower than normal because you do not have the PHP curl extension enabled.
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - tijsverkoyen/css-to-inline-styles 2.2.2 requires php ^5.5 || ^7.0 -> your php version (8.0.2; overridden via config.platform, actual: 8.1.3) does not satisfy that requirement.
    - tijsverkoyen/css-to-inline-styles[2.2.3, ..., 2.2.4] require ext-dom * -> it is missing from your system. Install or enable PHP's dom extension.
    - laravel/laravel v9.1.1 requires laravel/framework ^9.2 -> satisfiable by laravel/framework[v9.2.0, ..., v9.4.1].
    - laravel/framework[v9.2.0, ..., v9.4.1] require tijsverkoyen/css-to-inline-styles ^2.2.2 -> satisfiable by tijsverkoyen/css-to-inline-styles[2.2.2, 2.2.3, 2.2.4].
    - Root composer.json requires laravel/laravel 9.1.1 -> satisfiable by laravel/laravel[v9.1.1].

To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php/8.1/cli/php.ini
    - /etc/php/8.1/cli/conf.d/10-opcache.ini
    - /etc/php/8.1/cli/conf.d/10-pdo.ini
    - /etc/php/8.1/cli/conf.d/20-calendar.ini
    - /etc/php/8.1/cli/conf.d/20-ctype.ini
    - /etc/php/8.1/cli/conf.d/20-exif.ini
    - /etc/php/8.1/cli/conf.d/20-ffi.ini
    - /etc/php/8.1/cli/conf.d/20-fileinfo.ini
    - /etc/php/8.1/cli/conf.d/20-ftp.ini
    - /etc/php/8.1/cli/conf.d/20-gettext.ini
    - /etc/php/8.1/cli/conf.d/20-iconv.ini
    - /etc/php/8.1/cli/conf.d/20-phar.ini
    - /etc/php/8.1/cli/conf.d/20-posix.ini
    - /etc/php/8.1/cli/conf.d/20-readline.ini
    - /etc/php/8.1/cli/conf.d/20-shmop.ini
    - /etc/php/8.1/cli/conf.d/20-sockets.ini
    - /etc/php/8.1/cli/conf.d/20-sysvmsg.ini
    - /etc/php/8.1/cli/conf.d/20-sysvsem.ini
    - /etc/php/8.1/cli/conf.d/20-sysvshm.ini
    - /etc/php/8.1/cli/conf.d/20-tokenizer.ini
You can also run `php --ini` in a terminal to see which files are used by PHP in CLI mode.
Alternatively, you can run Composer with `--ignore-platform-req=ext-dom` to temporarily ignore these required extensions.

composer config platform.php 7.0

shigurechan@shigurechan-System-Product-Name:~/prg/html$ composer update
Composer is operating significantly slower than normal because you do not have the PHP curl extension enabled.
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Root composer.json requires ramsey/uuid 4.2.2 -> satisfiable by ramsey/uuid[4.2.2].
    - ramsey/uuid 4.2.2 requires php ^7.2 || ~8.0.0 || ~8.1.0 -> your php version (7.0; overridden via config.platform, actual: 8.1.3) does not satisfy that requirement.
  Problem 2
    - Root composer.json requires laravel/laravel 9.1.1 -> satisfiable by laravel/laravel[v9.1.1].
    - laravel/laravel v9.1.1 requires php ^8.0.2 -> your php version (7.0; overridden via config.platform, actual: 8.1.3) does not satisfy that requirement.

Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.